The renowned metal-oxide-silicon (MOS) device was set forth by Moll, Pfann and Garrett at 1959 as an epoch-making innovation. MOS device was originally designed for producing voltage-controlled capacitors. In 1970s, Boyle and Smith first put through a new concept of charge-coupling and thus made a charge-coupled device (CCD), which has become a crucial component in a digital still camera. In 1980s, MOS device has been widely used as a key element in integrated circuits (ICs). A CMOS (complementary metal-oxide-semiconductor) device that is comprised of an n-channel MOSFET (metal-oxide-semiconductor field-effect transistor) and a p-channel MOSFET plays a significant role in a very-large scaled integrated (VLSI) circuit or an ultra-large scaled integrated (ULSI) circuit. Consider the application of a solar cell, great importance is still attached to the known MOS device that makes the MOS device become a high-valued component.
Although the MOS device plays an extremely important role in microelectronic circuits, its application in light-emitting display device is not highly expected. This is because silicon is an indirect bandgap semiconductor, and the electroluminescent radiation which is carried out by the recombination process of electrons and holes requires the participation of phonons such that the momentum conservation principle can be satisfied. Under ordinary conditions, the probability in which electrons, holes and phonons collide with each other simultaneously is little, and thus the probability of the recombination of electrons and holes and also the possibility of the generation of electroluminescent radiation are quite insignificant. This narrows the prospect of the MOS device in the application of electroluminescent display device.
To conquer the foregoing weakness, a MOS light emitting diode (MOSLED) using nanoparticles and nanostructures is innovated that enhances the electroluminescent efficiency thereof by loosening the restrictions imposed by the indirect bandgap of silicon. The fundamental principle of the MOS light emitting diode is to utilize the tunneling effect based on the quantum mechanics. It is appreciated by applying the calculating formulas according to the quantum mechanics that the probability of the occurrence of the electron tunneling effect will be drastically increased as the thickness of the oxide is downscaled to the degree of several nanometers. This tunneling effect will be directly proportional to the forward-biased voltage applied to the MOS device. However, since silicon dioxide is not a conductor after all, a- non-negligible voltage will be present across the oxide layer. That is, the metal layer and the oxide layer are suffering different voltages, which in turn cause the energy band of silicon to bend. In case of a N-type silicon, the energy band of silicon in the proximity of silicon-oxide interface will bend downward under a forward-biased condition (a positive voltage is applied to the metal layer and a negative voltage is applied to the oxide layer), and thus form a potential well that collects a large number of electrons hereabouts. Meanwhile a large number of holes travels from the metal layer by way of tunneling effect to this potential well collecting a large number of electrons, so that a large number of electrons and holes are allowed to be recombined hereabouts and the electron-hole pair can be easily collided with phonons to make electroluminescent radiation. In case of a P-type silicon, the fundamentals of electroluminescent radiation and the generation of photons can be deduced by an analogous way with those of a N-type silicon.
However, because the electroluminescent radiation of the MOS light emitting diode is taken place at the surface of a silicon substrate, the recombination of electrons and holes is inevitably influenced by non-radiative recombination centers. These non-radiative recombination centers generally include impurities, defects, and surface states, and they are enabled to lower the percentage of radiative recombination. These non-radiative recombination centers referred herein provides an additional approach for electrons and holes to be recombined, and the lifetime of carrier including electrons and holes is significantly reduced because of the participation of these non-radiative recombination centers. Hence, if it is desired to improve an electroluminescent efficiency of a MOS light emitting device, the extent of non-radiative recombination centers has to be reduced and thus the percentage of radiative recombination can be enhanced.
In view of the foregoing, a plenarily innovative technique of producing a MOS light emitting device and improving an electroluminescent efficiency of a MOS light emitting device by etching a silicon substrate thereof is disclosed, which is possible to loosen the restrictions imposed by the indirect energy bandgap of silicon and improve the electroluminescent efficiency of the MOS light emitting device efficiently.